I'll translate few updates from the links below. Just to provide something better than google translation.
http://www.hurriyet.com.tr/gundem/22509010.asp
It says the reason for her death was the hit she got to her head.
They found receipts which add up to 15,000$ and this is just too much for her and her husband's (mentioned that he is a bus driver) income. They are now considering drug smuggling as it is fairly common that American women to be used to carry drugs from europe to turkey. It could be related to an international drug mafia which always use American women. Says women usually earn abou 10,000$ each time.
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http://www.haberturk.com/gundem/haber/816824-flas-sarai-sierranin-cesedi-bulundu
This one mentions both the stabbing wound and the wound in the head is the reason.
No signs of rape at the initial investigation.
Her husband diagnosed the body in the hospital. (so heart breaking, may she rest in peace)
There are 15 people which are in custody, including 2 women.
They will take blood and DNA samples from all this people. Also 4 homeless people who stay in that area has been interrogated to and released. (they weren't suspects, just taken for information)
*I believe it is same for other 15 people. Turkish police tend to put everyone around the crime scene into custody. So I am guessing that 11 were just hanging around. Thats usually why people don't report suspicious things.
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http://www.cnnturk.com/2013/turkiye....sierranin.cesedi.bulundu/694960.0/index.html
This one also says there was a blanket next to her. Thats why they believe the body has been moved. She was wearing blue jeans, jumper and a jacket. These are the same clothes from 21st and she had her jewelery on.